402 MARINE PRODUCTS OF COMMERCE 



long, and 30 feet or more high. In many commercial plants these may be in- 

 corporated within larger bnildings and are often two or three stories high. The 

 older types are constructed of wood, except possibly for the fire pit, which is of 

 brick. Other types are completely constructed of brick or other fireproof material, 

 which is more desirable for the smoking process since it eliminates the fire hazard. 

 Air-smoke circulation is maintained by natural draft; the fire pit is equipped with 

 dampers to control aii" intake, while adjustable louvers are located near the roof 

 to allow removal of surplus smoke and moisture-laden air. By these means air- 

 smoke circulation can be controlled to a limited extent, but is dependent consider- 

 ably upon external weather conditions, size of the fire, and height of the smoke- 

 house. 



Temperature and humidity are controlled to a limited extent by adjustment of 

 the dampers and louvers and size of the fire, but these factors also depend upon 

 prevailing weather conditions. In winter the smokehouse temperature may fall so 

 low as to require a fairly hot fire. An extremely hot fire causes too rapid and 

 complete combustion of the wood or sawdust, thereby reducing the quality of the 

 smoke for curing. In warm weather too low a fire may be necessary, causing a 

 dense wet smoke which also tends to produce an inferior smoked product. In some 

 of the larger towering kilns the fish nearest the fire are cured much faster than 

 those near the roof; considerable handling is therefore necessary to give a uni- 

 formly cured product. With the wood fire directly below the fish there is a 

 tendency for soot and flying ash to deposit on the fish, rendering the product 

 inferior. Despite the many disadvantages of the old-style smokehouses, excellent 

 products have been and still are being produced in them. However, this can be 

 accomplished only on a uniform basis by a seasoned and careful operator who 

 has had long experience with the particular type of smokehouse that is being used. 



Controlled Smoking. The preceding discussion on kiln smoking indicates that 

 few scientific principles have been applied to the process. Very httle attention 

 has been paid to the accurate control of each individual procedure involved. In 

 fact the very construction of the smokehouse makes accurate control difficult to 

 attain. There are four main variables in the smoking procedure which must be 

 subject to control. In the designs of the various so-called controlled smokehouses 

 attempts are made to incorporate all the equipment necessary to accomplish this 

 end. These variables are: (1) smoke volume and quality, (2) temperature, 

 (3) humidity, and (4) air velocity and distribution. 



The generated smoke must be clean and free of soot, grit, and ash. The genera- 

 tor may be located adjacent to or some distance from the smokehouse proper. It 

 should be equipped with suitable dampers and ventilators to insure proper com- 

 bustion of the wood and control of smoke density. A metal box or drum may be 

 used for the generator. The smoke must be dehvered to the house through a large 

 diameter pipe to allow for the condensation of tars and resins and to prevent 

 clogging due to deposition of these products. Traps for catching and draining these 

 materials should be located at convenient places along this pipe line. 



The smokehouse proper should be constructed of fireprgof material and suffi- 

 ciently insulated to keep any heat loss to a minimum. Some heat may be derived 

 from the smoke generator, but additional heating units should be installed in the 

 smokehouse to allow for accurate temperature control and for drying or cooking 

 the fish. Proper temperatures should be maintained by thermostatic control. 



